The availability of energy to power instruments/devices or equipment for different purposes is very important. For remote or unattended applications batteries or fuel cells are needed. The choice of power source for instruments and communication networks are dependent on the environment and power needs of the device. For equipment that is placed in remote locations, such as at the bottom of the ocean, or intended for long term deployment, power sources that run for a long duration are advantageous.
Work on fuel cells began in the early 19th century. Whereas batteries release energy stored in a closed system, fuel cells are energy conversion systems, transferring electricity from replenishing sources of external fuel. Fuel cells may produce electricity continuously if provided a sufficient flow of the external fuel, as opposed to batteries.
Microbial fuel cells are being developed to provide long-term power for a variety of applications for remote sensing and long duration studies. The cells are an attractive choice for this application due to the longevity of the cells. Microbial fuel cells convert chemical energy to electrical through a catalytic reactions, using microorganisms. The cells are comprised of two chambers separated by a cation exchange membrane. The anode chamber contains microorganisms in a microorganism-specific media. The media is a fed into the fuel cell where microorganisms catabolize the compound under anaerobic conditions producing carbon dioxide, protons, and electrons.
The second chamber is a cathode chamber, containing deionized (D.I.) water with an oxidizer. Typical microbial fuel cells use potassium ferricyanide/potassium hydrogen phosphate, oxygen, hydrogen peroxide, manganses dioxide, or copper chloride as the oxidizer.
Electrons gained from this process enter an electrical circuit, providing current. One drawback of microbial fuel cells is the low power output, due in part to electron transfer efficiency. Previous modifications to address this shortcoming have included electron mediators or mediatorless microbes. Redox mediators couple the electron reduction, through oxidative metabolism in a microbe, to the reduction of the electron acceptor on the cathode. (Zeikus, et al., U.S. Pat. No. 6,495,023, columns 3 and 4).
However, even with the advances made in microbial fuel cells, the process still produces only small electrical currents, far below the energy production of other fuel cells. What is needed is a more efficient electron transfer device.